Voltage drop

[desmo4]

My SPA gauge is powered from the under dash fuse box and when I compare it to my Fluke DVM across the battery, the voltage drop is sometimes as much as 1,5 volts lower than across the battery. This is measured with the engine running. So to get an accurate reading I am going to have to connect the SPA gauge directly to the battery through a relay. I am presently working out using the rear defroster circuit to switch the power on and off.

Jonathan

[repiv]

So is my Escort radar detector which has a voltage readout and like you pointed out to me some time ago, readings at the fuse panel can sometimes be "off" from what you would get across the battery terminals. For me, that's OK because I only need to know how the whole charging system is working at any given time and when it deviates from this, that's when I need to go do further investigations. I'm Ok with the daily fluctuations in voltage after the voltage regulator (Electronic Load Detector they call it on our cars).
If you're going to use a relay anyway to power the voltage pickup on your gauge, why not just use the HOT with ignition spade connector on the fuse panel to power the relay? That way you don't have to worry about turning anything else on just to get a voltage reading. Your I-Moni also has a voltage readout, too. I just never chose to wire it in since I have the Escort. I could also power the Escort using a relay to wire the thing directly to the battery as well, but I've gotten accustomed to knowing what the voltage fluctuations mean on a daily basis.